Forensic pathologist Corrie Swanson investigates a brutal crime from 136 years ago. The key to the crime may just lie in a lost Sherlock Holmes story, a tale allegedly so horrifying that its author never dared publish it.

A body is discovered, without its head - two killers are on the loose. A pair of killers requires a team of equally talented investigators. Luckily both Vincent D'Agosta and Special Agent Pendergast are back in town.